Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted to a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in length). In addition, the wind turbines are typically mounted on towers that are at least 60 meters in height. Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators that may be rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid.
During normal operation, wind turbines with sophisticated control system maintain constant speed and power by active blade pitch control. The initial design of a wind turbine controls may use standards such as IEC 61400. In the control configuration, the standardized environmental conditions such as average wind speed, turbulence intensity or air density are the basis for the design. The IEC standard defines a small number of different “type classes” that categorize a wind turbine design for broader range of environmental conditions. As such, the standard controller configuration fails to address all of the types of site locations on which the wind turbine may be installed.
For example, many wind turbine sites include more favorable environmental conditions that give less stress on the actual wind turbine than the design conditions. At these sites, it is possible to use this application to increase the wind turbine performance, using a higher average rotor speed, without damaging wind turbine components.
Therefore, what is needed is a method for operating a wind turbine that permits increased energy capture by controlling the rotor speed in response to measured or calculated operational parameters.